This invention relates to imaging media. In a preferred form, it relates to supports for photographic, ink jet, thermal, and electrophotographic media.
In order for a print imaging support to be widely accepted by the consumer for imaging applications, it has to meet requirements for preferred basis weight, caliper, stiffness, smoothness, gloss, whiteness, and opacity. Supports with properties outside the typical range for xe2x80x98imaging mediaxe2x80x99 suffer low consumer acceptance.
In addition to these fundamental requirements, imaging supports are also subject to other specific requirements depending upon the mode of image formation onto the support. For example, in the formation of photographic paper, it is important that the photographic paper be resistant to penetration by liquid processing chemicals failing which there is present a stain on the print border accompanied by a severe loss in image quality. In the formation of xe2x80x98photo-qualityxe2x80x99 ink jet paper, it is important that the paper is readily wetted by ink and that it exhibits the ability to absorb high concentrations of ink and dry quickly. If the ink is not absorbed quickly, the elements block (stick) together when stacked against subsequent prints and exhibit smudging and uneven print density. For thermal media, it is important that the support contain an insulative layer in order to maximize the transfer of dye from the donor which results in a higher color saturation.
It is important, therefore, for an imaging media to simultaneously satisfy several requirements. One commonly used technique in the art for simultaneously satisfying multiple requirements is through the use of composite structures comprising multiple layers wherein each of the layers, either individually or synergistically, serves distinct functions. For example, it is known that a conventional photographic paper comprises a cellulose paper base that has applied thereto a layer of polyolefin resin, typically polyethylene, on each side, which serves to provide waterproofing to the paper and also provides a smooth surface on which the photosensitive layers are formed. In another imaging material as in U.S. Pat. No. 5,866,282, biaxially oriented polyolefin sheets are extrusion laminated to cellulose paper to create a support for silver halide imaging layers. The biaxially oriented sheets described therein have a microvoided layer in combination with coextruded layers that contain white pigments such as TiO2 above and below the microvoided layer. The composite imaging support structure described has been found to be more durable, sharper, and brighter than prior art photographic paper imaging supports that use cast melt extruded polyethylene layers coated on cellulose paper. In U.S. Pat. No. 5,851,651, porous coatings comprising inorganic pigments and anionic, organic binders are blade coated to cellulose paper to create xe2x80x98photo-qualityxe2x80x99 ink jet paper.
In all of the above imaging supports, multiple operations are required to manufacture and assemble all of the individual layers. For example, photographic paper typically requires a paper-making operation followed by a polyethylene extrusion coating operation, or as disclosed in U.S. Pat. No. 5,866,282, a paper-making operation is followed by a lamination operation for which the laminates are made in yet another extrusion casting operation. There is a need for imaging supports that can be manufactured in a single in-line manufacturing process while still meeting the stringent features and quality requirements of imaging bases.
It is also well known in the art that traditional imaging bases consist of raw paper base. For example, in typical photographic paper as currently made, approximately 75% of the weight of the photographic paper comprises the raw paper base. Although raw paper base is typically a high modulus, low cost material, there exist significant environmental issues with the paper manufacturing process. There is a need for alternate raw materials and manufacturing processes that are more environmentally friendly. Additionally to minimize environmental impact, it is important to reduce the raw paper base content, where possible, without sacrificing the imaging base features that are valued by the customer, i.e., strength, stiffness, surface properties, etc. of the imaging support.
An important corollary of the above is the ability to recycle photographic paper. Current photographic papers cannot be recycled because they are composites of polyethylene and raw paper base and, as such, cannot be recycled using polymer recovery processes or paper recovery processes. A photographic paper that comprises significantly higher contents of polymer lends itself to recycling using polymer recovery processes.
Existing composite color paper structures are typically subject to curl through the manufacturing, finishing, and processing operations. This curl is primarily due to internal stresses that are built into the various layers of the composite structure during manufacturing and drying operations, as well as during storage operations (core-set curl). Additionally, since the different layers of the composite structure exhibit different susceptibility to humidity, the curl of the imaging base changes as a function of the humidity of its immediate environment. There is a need for an imaging support that minimizes curl sensitivity as a function of humidity, or ideally, does not exhibit curl sensitivity.
The stringent and varied requirements of imaging media, therefore, demand a constant evolution of material and processing technology. One such technology known in the art as xe2x80x98polymer foamsxe2x80x99 has previously found significant application in food and drink containers, packaging, furniture, appliances, etc. Polymer foams have also been referred to as cellular polymers, foamed plastic, or expanded plastic. Polymer foams are multiple phase systems comprising a solid polymer matrix that is continuous and a gas phase. For example, U.S. Pat. No. 4,832,775 discloses a composite foam/film structure which comprises a polystyrene foam substrate, oriented polypropylene film applied to at least one major surface of the polystyrene foam substrate, and an acrylic adhesive component securing the polypropylene film to said major surface of the polystyrene foam substrate. The foregoing composite foam/film structure can be shaped by conventional processes as thermoforming to provide numerous types of useful articles including cups, bowls, and plates, as well as cartons and containers that exhibit excellent levels of puncture, flex-crack, grease and abrasion resistance, moisture barrier properties, and resiliency.
Foams have also found limited application in imaging media. For example, JP 2839905 B2 discloses a 3-layer structure comprising a foamed polyolefin layer on the image-receiving side, raw paper base, and a polyethylene resin coat on the backside. The foamed resin layer was created by extruding a mixture of 20 weight % titanium dioxide master batch in low density polyethylene, 78 weight % polypropylene, and 2 weight % of Daiblow PE-M20 (AL)NK blowing agent through a T-die. This foamed sheet was then laminated to the paper base using a hot melt adhesive. The disclosure JP 09127648 A highlights a variation of the JP 2839905 B2 structure, in which the resin on the backside of the paper base is foamed, while the image receiving side resin layer is unfoamed. Another variation is a 4-layer structure highlighted in JP 09106038 A. In this, the image receiving resin layer comprises of 2 layers, an unfoamed resin layer which is in contact with the emulsion, and a foamed resin layer which is adhered to the paper base. There are several problems with this, however. Structures described in the foregoing patents need to use foamed layers as thin as 10 xcexcm to 45 xcexcm, since the foamed resin layers are being used to replace existing resin coated layers to the paper base. The thickness restriction is further needed to maintain the structural integrity of the photographic paper base since the raw paper base is providing the stiffness. It is known by those versed in the art of foaming that it is very difficult to make thin uniform foamed films with substantial reduction in density especially in the thickness range noted above.
A further requirement for useful photographic elements is to provide a surface for an image-forming emulsion or gel layer that has a particular smoothness that, after coating with gel or emulsion, has a xe2x80x9cglossyxe2x80x9d surface. A Gardner glossmeter can be used to measure the scattered light reflection from a surface; xe2x80x9cglossyxe2x80x9d surfaces typically reflect 40 % or more of the incident light so as to provide a shiny appearance.
Typical resin coated photographic paper, as currently made, utilizes the natural roughness of the raw paper base, as well as special chill rollers to obtain the required surfaces for control of gloss. The chill roller is used to form the melt extruded polyethylene plastic layer on raw paper base to get a very specific high performance surface.
There is a need for a composite imaging material base material that can be manufactured in a single in-line operation.
There is also a need for an imaging base that reduces the amount of raw paper base that is used.
There is also a need for an imaging base that can be effectively recycled.
There is also a need for an imaging base that resists the tendency to curl as a function of ambient humidity.
There is also a need for an imaging base that can supply a xe2x80x9cglossyxe2x80x9d surface when further coated by existing gel or emulsion systems.
There is also a need for an imaging base that can supply a particular surface that provides high speed coatability for existing gel or emulsion systems.
It is an object of the invention to provide a composite imaging material that meets the requirements of an imaging base, specifically with regard to features such as the basis weight, caliper, stiffness, smoothness, gloss, edge penetration, and opacity.
It is another object of this invention to provide a composite imaging material that resists humidity curl.
It is another object to provide an imaging member that can be manufactured in-line in a single operation.
It is a further object to provide an imaging member that can be recycled.
It is a further object to provide an imaging member that provides a base that is capable of a xe2x80x9cglossyxe2x80x9d surface.
It is a further object to provide an imaging member that provides a base that is capable of high speed coating of gels or emulsions.
These and other objects of the invention are accomplished by an imaging member comprising an imaging layer and a base wherein said base comprises a closed cell foam core sheet and adhered thereto an upper and lower flange sheet wherein said upper flange sheet comprises oriented polystyrene or polyolefin wherein the modulus of said upper flange sheet is between 1000 and 3500 MPa and the roughness of the upper surface of said base is less than 0.4 xcexcm Ra.
This invention provides a superior imaging support. Specifically, it provides an imaging support of high stiffness, precise smoothness for high gloss and coatability, high opacity, and excellent humidity curl resistance. It also provides an imaging support that can be manufactured using a single in-line operation. It also provides an imaging support that can be effectively recycled.